Automated bulk optical processing equipment can perform a variety of tasks such as, for example, inspection or sorting bulk articles including raw or processed fruit, vegetables, wood chips, recycled plastics and other similar products. The articles may be characterized according to size, color, shape or other qualities. Modern bulk optical processing equipment can rapidly separate very large quantities of articles into numerous categories.
Such equipment typically includes a conveyor belt that moves the articles past an inspection station where cameras or other detection devices examine the articles. The inspection station sends signals to a sorter or treatment station where the articles are sorted or otherwise treated by category. For example, defective or foreign articles may be removed from the flow of articles carried by the conveyor belt. Frequently, unacceptable articles are removed by directing an accurately timed blast of fluid, such as compressed air, at the article as it is projected from the conveyor belt in order to direct it out of the process flow. Separation takes place at a location in the transport system where the articles are unsupported so that defective articles can easily be removed from the stream. Acceptable articles are collected in a product outfeed location such as a product outfeed chute, while unacceptable articles are directed into a reject outfeed chute.
One type of system can be seen in FIG. 1 in which a processing system 10 employs a continuous conveyor belt 12 hung between an upper drive roller 14 and a lower end roller 16 so that the conveyor belt 12 has a catenary shape. Articles 18 are transferred to an upper surface 20 of the conveyor belt 12 from an infeed chute (not shown) at or near the drive roller 14. The slope of the conveyor belt 12 helps stabilize the articles 18 by centrifugal force as the articles 18 approach the end roller 16. The velocity of the articles 18 near the end roller 16 is approximately the same as the velocity of the conveyor belt 12. The articles 18 are launched from the conveyor belt 12 at the end roller 16 along a trajectory 22 past an inspection station 24 and an ejector 26 where the articles 18 are processed.
The articles are processed by directing an accurately timed blast of fluid, such as compressed air, at unacceptable articles as they are projected along their trajectory 22. The fluid is directed within a plane 28 through which the articles 18 travel. The time it takes the articles 18 to reach the plane 28 is determined by the angle of the trajectory 22. The trajectory 22 is slightly inclined from a horizontal plane 30 and forms an angle 32 therewith. Thus, the trajectory 22 of the articles 18 is prescribed by the angle of launch and the velocity of the articles 18.
The trajectory 22 lies in a plane extending from the belt surface near the end roller 16. Thus, the angle 32 of the trajectory 22 is dependent upon the position of the belt surface immediately adjacent the end roller 16. The position of the belt surface adjacent the end roller 16 is determined by the "sag" of the load-bearing top portion 34 of the conveyor belt 12 when it is suspended between the drive roller 14 and end roller 16. The amount of "sag" is dependent upon the fraction of the total length of the conveyor belt 12 that constitutes the load-bearing top portion 34 of the conveyor belt 12. If the conveyor belt 12 is lightly loaded as shown in solid lines in FIG. 1, a tensioning roller 36 bears upon a top surface 38 of a bottom portion 40 of the conveyor belt 12 and restricts the amount of the conveyor belt 12 that constitutes the load-bearing top portion 34. Thus, the "sag" of the conveyor belt 12 is minimal and the angle 32 is small producing a slightly inclined trajectory.
However, as the conveyor belt 12 becomes more heavily loaded with articles 18 as seen in phantom in FIG. 1, a greater portion of the conveyor belt 12 slides around the drive roller 14 and end roller 16 so that the "sag" increases. As the "sag" increases, so does the angle of the conveyor belt 12 producing a greater trajectory angle 32.
This variability of the trajectory angle has a detrimental effect upon the quality of the sort. The location of the linear field of view of the inspection station 24 is fixed as is the pattern of the air streams from the ejector 26. The in-air transit time of the articles 18 between the field of view of the inspection station 24 and the plane 28 of air streams from the ejector 26 is a critical parameter for effective sorting. Since the time of transit, location, and direction of the articles 18 at the plane 28 of the ejector 26 is highly dependent upon the angle of launch, a variable launch angle is undesirable.